C++ pointer is initialized to null by the compiler - pointers

Question

So I've been stuck on a memory problem for days now.
I have a multi-threaded program running with c++. I initialize a double* pointer.
From what I've read and previous programming experience, a pointer gets initialized to garbage. It will be Null if you initialize it to 0 or if you allocate memory that's too much for the program. For me, my pointer initialization, without allocation, gives me a null pointer.
A parser function I wrote is suppose to return a pointer to the array of parsed information. When I call the function,
double* data;
data = Parser.ReadCoordinates(&storageFilename[0]);
Now the returned pointer to the array should be set to data. Then I try to print something out from the array. I get memory corruption errors. I've ran gdb and it gives me a memory corruption error:
*** glibc detected *** /home/user/kinect/openni/Platform/Linux/Bin/x64-Debug/Sample-NiHandTracker: free(): corrupted unsorted chunks: 0x0000000001387f90 ***
*** glibc detected *** /home/user/kinect/openni/Platform/Linux/Bin/x64-Debug/Sample-NiHandTracker: malloc(): memory corruption: 0x0000000001392670 ***
Can someone explain to me what is going on? I've tried initializing the pointer as a global but that doesn't work either. I've tried to allocate memory but I still get a memory corruption error. The parser works. I've tested it out with a simple program. So I don't understand why it won't work in my other program. What am I doing wrong? I can also provide more info if needed.
Parser code
double* csvParser::ReadCoordinates(char* filename){
int x; //counter
int size=0; //
char* data;
int i = 0; //counter
FILE *fp=fopen(filename, "r");
if (fp == NULL){
perror ("Error opening file");
}
while (( x = fgetc(fp)) != EOF ) { //Returns the character currently pointed by the internal file position indicator
size++; //Number of characters in the csv file
}
rewind(fp); //Sets the position indicator to the beginning of the file
printf("size is %d.\n", size); //print
data = new char[23]; //Each line is 23 bytes (characters) long
size = (size/23) * 2; //number of x, y coordinates
coord = new double[size]; //allocate memory for an array of coordinates, need to be freed somewhere
num_coord = size; //num_coord is public
//fgets (data, size, fp);
//printf("data is %c.\n", *data);
for(x=0; x<size; x++){
fgets (data, size, fp);
coord[i] = atof(&data[0]); //convert string to double
coord[i+1] = atof(&data[11]); //convert string to double
i = i+2;
}
delete[] data;
fclose (fp);
return coord;
}

Answer 1

Corrupt memory occurs when you write outside the bound of an array or vector.
It's called heap underrun and overrun (depends on which side it's on).
The heap's allocation data gets corrupted, so the symptom you see is an exception in free() or new() calls.
You usually don't get an access violation because the memory is allocated and it belongs to you, but it's used by the heap's logic.
Find the place where you might be writing outside the bounds of an array.